1. Field of the Invention
The present invention relates to a sheet processing apparatus for processing sheets that are ejected from an image forming apparatus such as a printer or a copier. More specifically, the invention relates to a sheet processing apparatus having a sheet cutting mechanism.
2. Description of the Related Art
A number of proposals have been made conventionally about post-processing apparatus for binding a book using recorded sheets that are ejected from an image forming apparatus such as a printer or a copier and outputting the resulting book. Among those is a sheet post-processing apparatus that staples, on the center line, sheets that have been ejected from an image forming apparatus and are stacked, folds the sheets in half along the stapling line (saddle stitch), presses the folded sheets and cuts of their end portions, and outputs a resulting book.
FIG. 18 illustrates a conventional sheet post-processing apparatus. In the sheet post-processing apparatus 201 that is connected to an image forming apparatus 200, a sheet that is ejected from sheet ejection rollers 230 of the image forming apparatus 200 is accepted by inlet rollers 202 and then transported along a transport path 220 by transport rollers 203. The sheet is then moved through a U-turn transport path in which the transport path is extremely bend by using a turn roller 204 and a switching nail 205, and put into a stacker 206. A sheaf of sheets is thus stacked in the stacker 206. The stacked sheaf of sheets is positioned in its width direction by a positioning stopper 208 that can be moved up and down by rotation of a belt 207, and the sheaf of sheets is then stapled on the center line by a stapler 210. Subsequently, the positioning stopper 108 is moved upward, whereby the center line reaches the position of a folding blade 211.
A folding operation is as follows. Upon turning-on of a solenoid 216, the folding blade 211 is moved downward obliquely, whereby the sheaf of sheets is pressed against the sheaf-of-sheets ejection outlet 209 and starts to be folded. The folded sheaf of sheets is nipped between pre-press rollers 212 and further transported downstream. After the fold is made sharper by a press rollers 214, the sheaf of sheets is transported to a cutting position of a slide cutting device 213 and stopped there. A cutting blade of the slide cutting device 213 is moved downward, whereby end portions of the folded sheets are cut off in a guillotine-like manner with the cutting blade and a fixed blade. Resulting saddle-stitch books are stacked on a sheet ejection tray 215.
In connection with the above mechanisms, a technique is known in which a cutting portion is positioned in a state that a sheaf of sheets to be cut is nipped between the press rollers 214 and the sheaf of sheets is cut by lowering a sharp cutting blade of the slide cutting device 213, whereby a resulting saddle-stitch book is given a clear, accurate edge (e.g., refer to JP-A-2000-143081 (pages 5 and 6 and FIG. 1)). Another technique is known in which end portions of stapled and folded sheets are cut off by a sheet cutting unit such as the slide cutting device 213 in a state that the sheets bridge the sheet cutting unit and a sheet stacking unit such as the sheet ejection tray 215, whereby the installation area of the apparatus can be reduced by a sheet projection length (e.g., refer to JP-A-2000-103567 (pages 3 and 4 and FIG. 1).
Incidentally, in recent years, it has come to be desired that equipment be reduced in size and from the viewpoint of ecology it has come to be desired strongly that equipment be reduced in power consumption. This trend also applies to post-processing apparatus for image processing apparatus. The techniques of the above-mentioned patent documents employ the guillotine-type slide cutting device is used, which is superior in that the cutting operation is quick. However, because of the guillotine-type, a long stroke is needed for the cutting blade, as a result of which the apparatus is voluminous as a whole. Further, the cutting blade should cover the entire sheet width and hence is costly. Further, instantaneous cutting causes a high degree of load concentration, which requires a very large drive current and starting current. This is a problem that should be solved from the viewpoint of ecology. Still further, since the cutting device itself is large, the degree of freedom in determining its position in the apparatus is low; for example, the ejection outlet should be located low in the apparatus. It was difficult to provide sheet processing apparatus that are easy-to-use to users.
In view of the above, inventors developed and proposed a technique in which a cutter unit for cutting a sheaf of sheets by moving a rotating circular blade in a horizontal direction is provided in the main body of a sheet processing apparatus (Japanese Patent Application No. 2002-364918). Employment of this technique makes it possible to provide a sheet processing apparatus that is smaller in size and maximum power than in the case of using the conventional technique. The inventors have thereafter studied diligently and improved the this technique in terms of power consumption and ease of use to users while maintaining the cutting quality. The present application is to propose such technical items that were not described in the previous application.